Inorganic mercury is found in batteries and is used in the chemical
industry and it is produced from elemental mercury through the
process of oxidation. Inorganic mercury is the most common form
that is present in drinking water but is not considered to be
very harmful to human health, in terms of the levels found in
drinking water. However, kidney damage may result from exposure
to inorganic mercury through other sources.

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Organic mercury (primarily methyl mercury) is produced
by specific bacterial organisms in surface waters that
convert inorganic mercury into organic mercury, which
is the form of mercury that poses a significant threat
to human health. Methyl mercury is ingested typically
by fish and bioaccumulates both in the tissues of fish
and the humans that eat these fish. Large predatory
fish can contain as much as 100,000 times more methyl
mercury than the surrounding water medium. This form
is rarely present in drinking water but is a very common
contaminant in the tissues of fish and causes damage
to the nervous system as well as teratogenesis. Both
inorganic and organic mercury are considered to have
a more detrimental effect on children due to the fact
that both forms are more easily absorbed into their
system.

In 1974, the EPA established the Safe Drinking Water Act that set
specific guidelines on contaminants that are commonly found in drinking
water. However, it was not until 1992 that mercury, in particular,
became regulated. Both the Maximum Contaminant Level Goal and the
Maximum Contaminant Level were set at 2 parts per billion because
current technology allows public water suppliers to detect and remove
mercury levels that low. The monitoring of mercury levels must take
place every three months if the level is higher than the set guideline
and specific measures must be taken to reduce these levels if they
are exceeded persistently. Approved methods of removing mercury
from the drinking water supply are the following: Coagulation/Filtration,
Granular Activated Carbon, Lime softening and Reverse osmosis.